This invention relates to an aqueous dispersion of an organic peroxide. More particularly, this invention relates to an aqueous dispersion of an organic peroxide which possesses highly desirable shelf life and low viscosity and is useful as a polymerization initiator for ethylenically unsaturated monomers.
The suspension or emulsion polymerization of an ethylenically unsaturated monomer is generally carried out by using a colloid protecting agent and/or a surfactant for the purpose of ensuring production of a particular polymer possessing a desired particle size and using a polymerization initiator for the purpose of initiating the polymerization.
Recently, in the production of an ethylenically unsaturated monomer, large, automated continuous and closed equipment is used for the purpose of enhancing the productivity and preventing pollution of the environment by the toxicity of residual or wasted monomer.
As a polymerization initiator suitable for the method of production described above, an organic peroxide suspended or emulsified in water for ease of use tends to be more highly rated than the conventional solid or liquid organic peroxide from the standpoint of ease of handling and safety.
Now, examples of the aqueous suspension and the aqueous emulsion mentioned above will be cited below. In the specification of Dutch Pat. No. 75 03051, there is disclosed an aqueous suspension comprising water, a protective colloid agent, a water-soluble cellulose derivative such as methyl cellulose, a solid organic peroxide such as dibenzoyl peroxide, at least 0.2% by weight of a non-ionic surfactant having an HLB value of not more than 12.5, and further at least 0.2% by weight of a non-ionic surfactant having an HLB value of not less than 12.5 or 0.01% by weight of an anionic surfactant.
In the specification of Swedish Pat. No. 80 00669 is disclosed an aqueous suspension which comprises water, a protective colloid agent, a water-soluble cellulose derivative such as, for example, hydroxyethyl cellulose, a solid organic peroxide such as dicetyl peroxydicarbonate, and an ethoxylated nonionic surfactant having an HLB value exceeding 15 and possessing no cyclic inner ether bond.
In the specification of European Pat. No. 32,757 there is disclosed an aqueous emulsion comprising water, a protective colloid agent, a water-soluble cellulose derivative, a liquid organic peroxide such as di-(2-ethylhexyl)peroxy dicarbonate, a surfactant, and 2 to 20% by weight of an alkanol having one to four carbon atoms and/or an alkane diol having two to four carbon atoms.
These aqueous dispersions, however, have the following problems. First, when the aqueous dispersion has a low viscosity, it shows extremely poor shelf life and tends to separate into two layers. Second, in the case of the aqueous dispersion exhibiting relatively satisfactory shelf life, it acquires such high viscosity as to make the conveyance thereof with a pump rather difficult. Third, the colloid protecting agent and the surfactant to be used as a dispersion stabilizer impair the stability of the polymerization system, lower the conversion, and spoil the polymer quality.
For example, the polymer is forced to exhibit insufficient volume resistivity and assume a flattened shape.
In the circumstances, there is a need for developing an aqueous dispersion which possesses a highly satisfactory shelf life, allows smooth conveyance with a pump, and, as a polymerization initiator, refrains from impairing the physical properties of the polymer being formed.